The present invention relates to a voltage monitoring circuit, a test method therefor, and a voltage monitoring system.
In an existing secondary battery system for vehicle, plural battery groups each including series-coupled battery cells are coupled to configure a battery module, and a control device for monitoring the state of the battery cells of each of the battery groups is provided. An example technique of such a battery system is disclosed in Japanese Unexamined Patent Publication No. 2010-193589.
FIG. 12 shows the battery system 1 disclosed in Japanese Unexamined Patent Publication No. 2010-193589. The battery system 1 has battery cells BC1 to BC6 and a cell controller 2. The cell controller 2 has a battery cell controller IC1 and a Schottky diode Db associated with the battery cells BC1 to BC6.
The battery cell controller IC1 includes a multiplexer (MUX) 11, a voltage regulator circuit 12, a differential amplifier 13, an analog-to-digital converter circuit (hereinafter referred to as an “ADC”) 14, an IC control circuit 15, diodes D1 and D2 for ESD protection, and terminals CV1 to CV6, VCC and GND. The terminals CV1 to CV6 and GND are coupled, via sensing lines SL, to the positive electrodes and negative electrodes of the battery cells BC1 to BC6. The sensing lines SL are provided between the positive and negative electrodes of the battery cells BC1 to BC6 and input terminals IN1 to IN7 provided on the circuit substrate side.
The multiplexer 11 has terminal voltages of the battery cells BC1 to BC6 inputted thereto via the terminals CV1 to CV6 and GND. The multiplexer 11 selects one of the terminals CV1 to CV6 and outputs the corresponding terminal voltage to the differential amplifier 13. The terminal GND serves as a ground terminal (hereinafter referred to as the “ground terminal GND”) for the battery cell controller IC1. The terminal VCC serves as a supply voltage terminal (hereinafter referred to as the “power supply terminal VCC”) for the battery cell controller IC1. The multiplexer 11 uses the voltage supplied from the power supply terminal VCC as a supply voltage.
The differential amplifier 13 amplifies the terminal voltage received from the multiplexer 11 and outputs the amplified voltage to the ADC 14. The ADC 14 outputs the inputted voltage after analog-to-digital conversion. The digital signal outputted from the ADC 14 is stored in the IC control circuit 15 and is used, for example, for diagnosing the battery system 1. When a fault is detected, it is eventually reported to a higher-level controller.
The voltage regulator circuit 12 provides the differential amplifier 13, ADC 14 and IC control circuit 15 with a supply voltage. The voltage regulator circuit 12 is coupled, via a line, to the terminal CV6. The voltage supplied from the terminal CV6 is used as a bias voltage for the voltage regulator circuit 12.
For all of the terminals CV1 to CV6, diodes D1 and D2 for ESD protection are coupled between the power supply terminal VCC and the ground terminal GND.
If the Schottky diode Db is not provided, disconnection of the lowest-order sensing line SL causes the current used by the battery cell controller IC1 to flow from the ground terminal GND to the positive electrode side of the battery cell BC6 via the diode D2 for ESD protection and the terminal CV6. As a result, the terminal CV6 is negatively biased corresponding to a voltage drop (0.6 to 0.7 V) through the diode D2 for ESD protection causing the voltage regulator circuit 12 to stop operation. When the voltage regulator circuit 12 stops operation, the differential amplifier 13, ADC 14 and IC control circuit 15 also stop operation, so that detection of a fault cannot be reported to a higher-lever controller.
To prevent the above problem, the battery system disclosed in Japanese Unexamined Patent Publication No. 2010-193589 is provided with a Schottky diode Db smaller than the diode D2 for ESD protection. With the voltage drop through the Schottky diode Db being as small as 0.3V, the negative voltage applied to the terminal CV6 in the event of disconnection of the lowest-order sensing line SL described above can be reduced to allow the voltage regulator circuit 12 to continue operation. Hence, when a fault is detected, it can be normally reported to a higher-order controller.